Pigment pastes containing water-soluble diisobutylene-maleic anhydride copolymer salts



United States Patent PIGMENT PASTES CONTAINING WATER-SOLU- BLE DlISOBUTYLENE-MALEIC ANHYDRIDE CO- POLYMER SALTS No Drawing. Application October 14, 1958 Serial No. 767,086

8 Claims. (Cl. 260-295) This invention deals with aqueous dispersions. of pigments, including extender pigments, particularly dispersions of such pigments in the form of aqueous pastes which are suitable for addition to aqueous resin dispersions to form water-base coating compositions. More specifically this invention concerns aqueous pigment pastes in which finely divided pigment (including organic as well as inorganic pigments, especially carbon black and calcium hydroxide which are diflicult to disperse) is maintained in a dispersed state with a small amount of a water-soluble salt of a low molecular weight, relatively homogeneous copolymer of maleic anhydride and diisobutylene of the formula CH2. This application is a continuation-in-part of copending applications Serial Nos. 373,660; 373,661; and 373,662, all filed August 11, 1953, and all now abandoned.

The need for well. dispersed pigments has long been recognized. For this purpose various agents have been proposed. Of these but few exhibit a high order of activity and then usually activity is confined to a narrow class of solids. As a rule, dispersants are quite specific in their action,-.any given agent providing dispersing activity-with a rather limited number of specific pigments and being markedly less effective or even ineffective with others.

Some materials acting as-dispersants for some specific sub- 40 stancemay be agglomerants for other substances.

There is thus a real need for dispersants which provide a high dispersing action for as many common pigments as possible and which at the same time will not exhibit incompatibilities with other pigments or other ingredients which are to be mixed therewith. The copolymers herein described have been found to possess this desirable combination of properties, acting on a great variety of pigments with good efficiency to provide dispersions useful in many types of applications and particularly for incorporation into water-base coatings.

Various copolymers of maleic anhydride and olefinically unsaturated bodies, including hydrocarbons, are known. They have been used, for example, in coatings, as agglomerating agents, and as binders. For purposes of agglomerating or binding it is necessary that the copolymers have high molecular weights, for example, of the order of 30,000 to 150,000, and in any case of more than 10,000.

Copolymers of this type have been the more usual.

But it has also been shown that copolymers of lower organic systems. If the high molecular weight copolymers are rendered water-soluble, they still act as binding .agents. -While they can be mixed with finely divided solids, they are not highly efiicient dispersants. Before 2,930,775 Patented Mar. 29, 1960 ice a suflicient amount of such material canabe added to give good dispersion in a pigment paste, a viscous composition results. The dispersing-efliciency of copolymers useful for binding is low. i

It was surprising, therefore, to discover that fluid pastes of high solids content and low water. content could be prepared by incorporating in a mixture of pigment, particularly one or more inorganic pigments, and water a relatively small amount of a water-soluble salt. from a copolymer of maleic anhydride and diisobutylene, which copolymer has a molecular weight of less than about 5,000 and which is relatively homogeneous, as shown by relation of molecular weight and viscosity of solutions thereof. The amount of salt of a low molecular weight, homogeneous copolymer effecting dispersion of solidand fluidity of the pigment paste will usuallynot-be over three percent of the weight of inorganic pigment and may be as low as about 0.05%. The preferred amounts for most pigments are usually from 0.1% to 1%. However, with carbon black and calcium hydroxide the proportions are generally between 0.5% and 4% With carbon black, the preferred proportion is usually between 2% and.3%; whereaswith calcium hydroxide, the preferred proportion is generally between 1.5% and 2%.v In this respect also the pigment pastes of this invention'differ from previously known coatingand binding copolymers, providing highly. efficient dispersing action at such low concen'tra tions that well dispersed pigment pastes are obtained long before any thickening .elfect is imparted from a high concentration ofcopolymer. a

The pastes here prepared will have a pH value of at least 4.5. andpreferably above seven. The range. of seven to eleven is preferred, although pastes-at pH .12 can be prepared which provide excellentdispersion of-solids.

It is besttto prepare pigment pastes with a. solids content from 50 to 85% and preferably 60 to 85%, as high a proportion of pigments being used as will permit fluidity. With carbon blacks, however, the more usual solids content is generally in the range of 20 .to50%. There will 'thus be at least 15 water in a paste, the water being M Ma where M and M are cations giving water-soluble c'arboxylates with a pH in water of at least-4.5. When am monia or amines are used for neutralization, either -di-' salts or mono-salts of the half-amide (malearnic acids) can be formed depending'upon the conditions of neutralization (the mono-salts of half-amides generally being formed at temperatures from room temperatureup to 50 C. to C. and the di-salts being formed at higher tern peratures) and both types are useful herein.

are sufliciently described in the art., Diisobutylene, which does not tend to form polymers by itself, reacts with maleic anhydride in a 1:1 mole ratio in the presence of a H polymerizing catalyst or initiator to form without par-' ticular precaution copolymersof low molecular size or of These are particularly a low degree. of polymerization, desirable copolymers because they canjreadilyj liq pared in a relativelyhomogeneous state, An "i'rr such as benzoyl peroxide, lauroyl peroxide, umene' y- Methods for copolymerizing-maleic anhydride and diisobutylene" 3 droperoxide, tert-butyl perbenzoate, or the like can be used.

Thus, copolymers can be prepared with molecular weights from 750 to 5,000. The molecular weights found will, of course, be average values. In this range of molecular sizes, it is possible to determine apparent molecular weights from colligative properties, such as boiling point elevation. But not all preparations of copolymers which have apparent molecular weights within the required range are efiicient dispersants for pigments.

Molecular weights can be readily determined from boiling point elevation by any method in which relatively small temperature differences can be accurately measured. A suitable method is based on use of the Menzies-Wright ebulliometer, particularly as modified by Hanson and Bowman, Analytical Edition (Ind. Eng. Chem. 11, 440 (1939)). Sensitivity and accuracy are further improved by use of a thermocouple in place of the vapor thermometer. The potential differences may be electronically amplified and recorded, if so desired, there being a number of amplifiers or electronic potentiometers and recorders available for this purpose. Acetone is a suitable solvent for dissolving samples of the copolymers. Extraneous factors can be eliminated by standardizing the method with benzil and by comparing substances of unknown molecular weight to it.

It has been found that etficient dispersants of the type here discussed must also have a homogeneity which is measured by the relationship of apparent molecular weight and viscosity by solutions. Thus, a copolymer for use as an efficient dispersant must not impart a viscosity of more than 1,000 cps. at 25 C. to solutions of its anhydride form at concentrations of 35% in an organic solvent such as dioxane or methyl ethyl ketone. This requirement eliminates mixtures of copolymers which contain some very large molecules and sufficient monomer and/or sufiicient very low polymer to bring the apparent molecular weight to a range which might appear to be useful, such heterogeneous mixtures having been found not to be efficient. By the same token unreacted starting materials should be absent or removed, as by stripping under reduced pressure and/or washing with water. The term homogeneous is here used to define copolymers meeting the above requirements; that is with a narrow distribution of copolymer sizes.

The defined copolymers of maleic anhydride and diisobutylene are taken up in water and treated with sufficient base, such as an alkali metal hydroxide, carbonate, or bicarbonate or ammonium hydroxide or the eyuivalent including quaternary ammonium and amine bases, to yield a soluble salt form which gives a pH of at least 4.5. When ammonium hydroxide is used, the salt formed may contain amide units as well as ammonium salt units. The copolymers are most conveniently used in solution, but for purposes of handling and shipping, the salts may be prepared in a solid form, in which case it is best to dissolve them prior to forming pigment pastes.

The defined copolymers are more effective dispersing agents for a greater variety of finely divided solids than any commercial products available up to the time of this research work. At a given solids content they give pastes of greater fluidity and with some solids they give fluid pastes with higher solids content than has heretofore been possible.

The copolymers of maleic anhydride and diisobutylene have inherently an optimum balance of hydrophobic and hydrophilic groups for intended applications. They are effective dispersants for an unusually wide variety of solid particles. They are highly effective with these in low proportions. Since the copolymers are essentially colorless, they do not impart color or off-colors. They are low in cost.

As inorganic white pigments and extender pigments there may be mentioned white lead, zinc oxide, titanium pigments, lithopone, other zinc sulfide pigments, barium sulfate, calcium carbonate, silica, talc, mica, and clays, such as china clay. Pigment pastes normally comprise one or more of these or equivalent pigments. There may also be used one or more insoluble, inorganic or organic pigments, such as an iron oxide, carbon black, cadmium sulfide, toluidene red, lithol toner, chrome orange, chrome yellow, Hansa yellow, chrome green, phthalocyanine green, phthalocyanine blue, etc. When a hydrophobic color is to be used, such as a Hansa yellow, it should be first wet with a solution containing a small amount of a wetting agent, an agent such as a sulfated alcohol, sulfonated alkylbenzene, sodium alkylphenoxypolyethoxyethyl sulfonate, or alkylphenoxypolyethoxyethanol, for the copolymers used in this invention are not wetting agents and do not exhibit significant capillary activity. Valuable dispersions of calcium hydroxide can also be made. A wide variety of carbon blacks has been found to respond to the dispersing action of the defined copolymers in salt form. Gas blacks are of primary importance and of these furnace blacks are of particular interest. Yet lamp blacks respond to the dispersing action as Well as acetylene black. As the particle size of these various blacks decreases, the amount of dispersant to give a maximum effect, in general, increases.

The term pigment is here used to cover a powder or powdered substance which is mixed with liquids to form paints, enamels, other coating compositions, or the like, which are insoluble therein, and which provide covering, hiding, filling, and/or coloring action. Since aqueous suspensions or dispersions of pigments are here dealt with, it is necessary that the dispersed pigments be insoluble in water. They are, of course, in the finely divided forms which are provided in commerce. Pigments are frequently ground or precipitated in a form to pass a 325 mesh screen.

For the preparation of pigment pastes, as has been indicated, it is generally most convenient to prepare an aqueous solution of copolymer in salt form. Concentrations of 5 to 40% may be used, although those of 10 to 20% are usually preferred. Pigment, water, and solutions are mixed. If desired, the paste or suspension may be ground in a milla pebble mill, roll mill, colloid mill, or high speed stone mill, or in some instances a high shear mixer being suitable. Sufficient copolymer is used to ensure good dispersion and fiuidity of the paste. The optimum amount of copolymer will depend upon the specific pigment or pigments and upon the state of subdivision thereof. In general, the finer the particle size the more dispersing agent should be used. Concentrated pastes can be extended to give dilute pastes, when the latter are needed.

Calcium hydroxide or so-called hydrated lime can be dispersed in water with the aid of the water-soluble salts of copolymers of maleic anhydride and diisobutylene having a molecular weight of 750 to 5,000, to give pastes or suspensions which are smooth, uniform, stable, and fluid. Furthermore, fluid pastes can thus be prepared with a higher solids content than has heretofore been possible. This is of advantage in handling, pumping, transporting, and using slurries of calcium hydroxide. These are useful for coatings as white-wash, field markings, or the like. They are also useful as concentrated alkaline reagents in chemical manufacturing.

The carbon black dispersions of this invention will have a pH between 7 and 12 and preferably between 9 and 11. When a dispersion of carbon black formed at an alkaline pH is brought to a lower pH, the dispersed carbon can be released or precipitated. This is of considerable importance, for example, in the compounding of rubbers in latices. The dispersions of carbon blacks in aqueous media are useful in the fields of paper, cement, water-base paints, coating compositions, inks, rayons, and rubber.

Fluidity titration tests were made with hydrated lime with different copolymer salts as dispersants. In these tests hydrated lime and water were mixed to form a anaemia stitfi paste, .which .wasititrated with small: incrementsof an; aqueous; 10%: solution :of: axcopolymerz. salt until;

fluidity resulted. The mixture was stirred afterzeach; incrementxwith a high speed mixer and examined for fluidity. The average solids content in these. tests was 53%; Fluidpastes .were prepared containingslj to 2.0% of-sthe sodium salts of copolymers of 'rnaleic :anal hydride-and. diisobutylene, thev anhydrides':havingxnumben average moleculariweights' of about .750, 1,000, and-4,000,

andhavingcviscosities as 35 solutions in dioxane of :32, 100*,aandi560cpzat 25" C. respectively. Thesepastes, even after storingfor six months, were still-'fluid-afterbeing-lrestirred. Yet when these pastes are -diluted and' applied as White-washto concrete surfaces; films --forrn=-- which -i rapidly become water-resistant, Withoutaddition of one ofthe above-defined copolymer salts, pastes of hydrated lime lose fluidity at 40 to 45% solids. With a few percent of one of these salts, however, fiuidpastes are obtainedup to55 to 60% solids.

Fl'uidity titration tests were made with a high abrasion furnace black; havinga'particle size of about 0.036 mieron and giving a pH-of 9.5 in aqueous suspension,- using difierent copolymer salts as dispersants. In' these tests carbon and water were-mixedto form-a-stiff paste, which was titrated with'small increments of'an aqueous 4 10% solution of a salt until fluidity resulted. The mixtime was' stirred after each increment with a high speed mixer. At the 'apparent end point the pastewasstirred for two minutes and left standing for fivemimites. If fluidity was not then maintained, titration was continued with small increments until fluidity could 'heso'mainta-ined. The average solid content of'the resultingpaste was-24%. Fluiditvwas obtained at the followingper centages of dispersant based on the weightof'carbon':

2.5% with the Na salt form of' a 1:1 copolymer'of35 maleic'anddiisobutylenegiving a pH of 11.3,- and "havin'gga number average molecular weight of about750, and'imparting to a'35% solution of the copolymer'in anhydr'ide formindioxane aviscosity'of 32 cp:'at*25 C.'; 2.2%withthe Na salt form of a 1:1 copolymer of" maleic and diisobutylene giving a pH of 11.7, and havinga number average molecular weight of "about 1,000, and imparting to'a"35% solution of'the copolymer in anhy' dride form'in dioxane a viscosity 'of'100'cp. at 25! CI; 2.8%'*with the 'Na salt form of a 1:1 'copolymer of maleic anddiisobutylene giving a pH' of 11.0, and having a number average molecular weight of about 4,000,and" imparting to a'35% solution of the copolymer in'anh'ydfide form in dioxane a viscosity of 560cp. at 25"CI;' 2.2% withthe K salt form of a 1:1 copolymer of inaleic and diisobutylene' giving'a pH'of-'9.'8 "and imparting to .a 35% solution of the copolymer in 'anhydr'ide form in dioxane a viscosity of 125 cp. at '25 C.; 2.2%. with the.

diisobutylene 'givin'g'a' pH'o'f' 9.8' and imparting to a solution- 'ofcopolymer in anhydridefor'm "ifidioxzin'l a viscosity 'of'130'cp7 at '25 C;

The 'maximum'amo'unt" of "carbon black whichcan be iucorporatedintoa fluid paste will, as'h'a'sb'een explained, dependupoir'particle"size: In general, this amonn'uis 30 to 40%"for'furna'c'e "blacks with amountsup to 3.5% of'a'salt' from'a defined 'co'p'olym'er being used. Coarser' carbon bla'cks' 'permitg0ing 'to" a total" solids of"ab'out in'a fluid paste:

In the study of the dispersantsandthefollowing pigment pasteswrheological.measurements were made with a stormer viscosimeter which .had been modified as su-g--' gestedzby- Fischer and Lindsley (Textile Res. J. XVIII 325, 1948); Weighed amounts of solid and water were treateiwith a solutionof a dispersing agentjusually forf convenience at 10% and at a H: 01595. Each mixturewas stirred fOr five-minut'es and left standing fo'r- 16 hours, care being taken to keep containers'capped to prevent losson moisture. The: mixture was then' stirred for five-minutes and brought to a=constant temperature; 30'

value at 'pigment content;

Itmight be noted thatthis iron-*oxide'was of very fine p article -sizenfless :than 0.1-micron). This fact limited theramount ofi pigment'whiehicould b'e used im a fiiiid paste. Oxides with coarser particles canbe used in pastes v at higher solids with retention of fluidity with any of the defined copolymer salts.

TABLE Calicum carbonate suspensions Copoly Pigment, Weight, Viscos-. Yield Kind men; Percent. g. ity, point, Percent poises g. r

None; 440- 0. 02 car 340-- The above calcium carbonate has "a par'ticle si ie'y'of j 6" C. Measurements were-tmadelini the conventional way. With good dispersions the instrument. quickly came to equilibrium and essentially identical :rate ofshear-shear force curves were obtained for increasing; or decreasing .1 loads. Forundisp'ers'ed or; poorly dispersed suspensions equilibrium was reached, if at all,with considerable difficulty. Typical dataare summarizedin 'th'e"'following" tablesa A i In successive columns therein there {are shown the par-. ticular copol-ymer studied, the percent of copolyinenbasd on the weight of "the pigment, the percent of pigment inthe mixture, the weight required is give 3001 1111. at 30 C., the apparent viscosityof' the suspension, and the yield point, if any. Where theayieldlpoint is shown as less than 10 grams, itcan beconsidered-that there is no yield-point-and-the-flow-is=dilatant. The friction of the instrument required two to three grams;

TABLE 1 of maleicuanhydride anddiisobutylene, :the1copolymerl-a havinga :molecular weight-of about 1,000 (number aver-1 age); The viscosity-10f a 35% solution .of thiscopolymer in- ;anhydride :form' in. dioxane-vwa's wcps' at 25 C The :copolymen was converted I to. a.--sodiumsalt, .a1110%' solution-thereof having a.-.pHJof -9.5.

Inthese viscosity ';determinations-'1-there were fused a cup of -1.375..inches diameterand a bob 'having asdiameter of 1.232 inches and:a height of 1.388-inches.

Red zirdn aocide i'SHSPhSiOfl-S O0poly+ Pigmenn Weight, Viscos- Kind Pmer, t Percent g. iy. ercen po ses None 30, 90. 0.14..

50 The yield point of the control; the sample wnhoue SEIighQduHO measunable zyieldxpoint, values of:=le'ss than 11 ,lOfgramstbeihg 'found,'.-or les's'thanethe lowest measur'able The kaolin used above had an average particle size of one to two microns with about 9% less than 0.2 micron.

Fluidity titration data given in the following Tables 6 and 7 were obtained from a variety of pigments with different copolymers. In this method of test a paste of pigment was titrated with small increments of an aqueous solution of a salt from a copolymer until fluidity resulted. The mixture was stirred after each increment with a high speed mixer for about a half-minute and examined for fluidity. Typical titration data are summarized in Table 6, where there are shown in the first column various pigments and in succeeding columns under each copolymer (1) the percent of copolymer on pigment and (2) the final percent of pigment in each mixture. This percent of pigment is not, however, the highest which can be reached with retention of fluidity.

TABLE 6 Fluidity titration data Copolymer A Copolymer A Oopolymer A Pigment Percent Percent Percent Percent Percent Percent Solid A Solid A Solid Zinc oxide All of the above copolymers were prepared from equimolar amounts of maleic anhydride and diisobutylene. Copolymer A has a molecular weight of about 1,000; A of about 750; A of about 4,000. Viscosities at 25 C. of 35% solution in dioxane are 100 cps., 32 cps., and 560 cps. at 25 C., respectively. The copolymers are all used in the form of sodium salts. Ammonium salts give at least as favorable results.

TABLE 7 Comparison fluidity data Product I is a sodium polyphosphate, which is an excellent dispersant for many solids, but is sensitive to pH, and heat.

Product II is a much used, commercial sulfonate, generally considered to give high dispersing activity.

The effectiveness of the copolymers of maleic anhydride and diisobutylene may also be demonstrated with data showing the maximum amount of a given pigment which may be taken up in water to form a paste having some degree of fluidity. The maximum is determined chiefly by the particular pigment examined and its particle size. As size decreases, surface area, of course, increases and use of somewhat more dispersant becomes necessary, particularly to reach an optimum state of dispersion.

Pastes of typical pigments were made in water and the maximum of pigment determined at which fluidity was observed. With blanc fixe the maximum was 80 to 85%, 0.25% of the disodium salt from a copolymer of maleic anhydride and diisobutylene being used. With zinc oxide (U.S.P. XII) the limit was likewise 80 to 85% at 0.25% of the same salt. With kaolin a limit of 70 to was found, also at 0.25 of the same salt. A limit of to of calcium carbonate was found where the particle size was two microns, 0.25% of the same salt also being used. With a calcium carbonate having a particle size of 0.2 micron, however, the upper limit was reached at 70 to 75% and an increase to 1% of the dispersant salt was found desirable. Almost identical data are obtained when other defined copolymers are substituted for that used above.

The defined copolymers are highly effective, as has been shown, against a great variety of pigments. For this reason they are particularly desirable in the preparation of the usual pigment pastes which are employed in coatings, since these are desirably composed of a number of pigments. A typical formulation comprises 250 parts of a titianum oxide pigment of the rutile type, 75 parts of lithopone, and parts of mica. To this mixture there is added 1.3 parts of the sodium salt from a copolymer of maleic anhydride and diisobutylene having a molecular weight of about 2,000. The mixture is quite fluid with enough water to give a paste of 65 to 70% solids. This is an entirely suitable pigment paste for addition to latices of copolymers, such as styrene and butadiene, vinyl acetate, acrylic resins, or other filmforming water-base resinous vehicles. Because of the efliciency of dispersion of the various solids in the pastes a higher ratio of pigment to binder can be safely used than has heretofore been practical. This is of particular importance in the coating of paper.

Other typical formulations for pigment pastes suitable for use in water-base paints are:

The pigment paste is treated with an aqueous solution of 1.2 to 1.5 parts of a sodium, potassium or ammonium salt from a homogeneous 1:1 copolymer of maleic anhydride and diisobutylene of correct molecular size and viscosity to give pastes useful for pigmenting a resinous dispersion. The pigment paste can readily be used with pigment/binder ratios from 1:2 to 4:1 with good dispersions of resins to give smooth, even coatings. For sealers on porous surfaces and for paper coatings pigment/binder ratios up to 20:1 and even 30:1 are feas- 9' ible, where; as here, the pigment "pastes-areeffectively anih efiici'ently dispersed.

Colored. pigment pastes are illustrated were following formulation:

The dispersant-was the sodium salt from the copolymer of maleic anhydride and diisobutylene, having a molecular weight of about 1,000 and giving a viscosity in a 35% solution in dioxane of 100 cps. at 25 C. This pigment paste was readily taken up in aqueous suspensions of resins to give water-base paints of good properties.

The pigment pastes of this invention are characterized by excellency of dispersion of inorganic pigments with or without colored pigments in a small amount of water. The high solids content of these pastes, between 50 and 85%, is attained with retention of fluidity. This desirable result is achieved with the aid of low molecular weight, homogeneous copolymers of maleic anhydride and diisobutylene which are converted to a salt form giving a pH of at least 4.5 and preferably of at least 7. The copolymers must have molecular weights below 5,000. They are used in amounts of 0.05% to 3% of the weight of the pigments except in the cases of carbon black and calcium hydroxide for which the amounts of copolymer salts desired may in some cases be as high as 4%.

The pigment pastes meeting the above requirements are readily and effectively incorporated into aqueous resin dispersions. They permit the fullest utilization of the hiding and covering power of pigments and pigment extenders. They bring out the maximum color of colored pigments. They provide better uniformity of pigment mixtures. They permit use of a higher pigment concentration in aqueous base coatings than has heretofore been possible.

We claim:

1. A pigment paste comprising an aqueous suspension of finely divided water-insoluble pigment dispersed with at least about 0.05%, on the weight of pigment, of a polymeric dispersant consisting of a water-soluble salt selected from the group consisting of ammonium and alkali metal salts of a polymeric material selected from the group consisting of a relatively homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 centipoises at 25 C., the suspension having a pH of at least 4.5 to 12.

2. As a composition of matter, a suspension of finely particled water-insoluble pigment in water, said pigment being dispersed with at least 0.05% to 4%, on the weight of pigment, of a polymeric dispersant consisting of a water-soluble salt selected from the group consisting of ammonium and alkali metal salts of a homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected '10 from t11e' class: consistingof dioxane "aiid'nie'tlryl: ethyl ketone arise-risky less than 1 ,000 eentipoises'at 25", 6., thes'uspensibn'having a; pH: between '7 and 1.1.

3.:A's a 'eomposition "of matten'a fluid paste of finely particled. water-insoluble pigment in water,- said pigment being present in said paste in an a'mount 'up to by weight of the .paste, and being dispersed with at least 0.05% 'of the weight of pigment of a polymeric dispersant consisting of a water-soluble salt selected from the group consisting of ammonium and alkali metal salts of a homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 centipoises at 25 C., said suspension having a pH between 7 and 11.

4. As a composition of matter, a suspension of finely divided water-insoluble inorganic pigment dispersed in water with a dispersing amount between 0.05% and 1% based on the weight of the pigment of a polymeric dispersant consisting of a salt selected from the group consisting of ammonium and alkali metal salts of a polymeric material selected from the group consisting of a homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 'centipoises at 25 C., said suspension having a pH between 7 and 11.

5. As a composition of matter, an aqueous dispersion of carbon black having a pH from 7 to 12, said carbon black being dispersed by 0.5% to 4%, on the weight of carbon black, of a polymeric dispersant consisting of a water-soluble salt selected from the group consisting of ammonium and alkali metal salts of a homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 centipoises at 25 C.

6. As a composition of matter, an aqueous dispersion containing up to 60% by weight of finely divided calcium hydroxide and having a pH in the range of 7 to 12, said hydroxide being dispersed with 0.5 to about 4% by weight, on the weight of the hydroxide, of a polymeric dispersing agent consisting of a water-soluble salt selected from the group consisting of ammonium and alkali metal salts of a polymeric material selected from the group consisting of a copolymer, having a molecular weight between 750 and 5,000, of a mixture consisting of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material giving a viscosity of less than 1,000 cps. at 25 C. in a 35 solution in an inert organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone.

7. As a composition of matter, a suspension of finely particled water-insoluble pigment in water, said pigment being dispersed with at least 0.05 to 4%, on the weight of pigment, of a polymeric dispersant consisting v of awater-soluble sodium salt of a homogeneous copolymer, having a molecular weight between 750 and 5,000, of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 centipoises at 25 C., the suspension having a pH between 4.5 and 12.

8. As a composition of matter, a suspension of finely particled water-insoluble pigment in water, said pigment being dispersed with at least 0.05% to 4%, on the weight of pigment, of a polymeric dispersant consisting of a water-soluble ammonium salt of a homogeneous copolymer, having a molecular weight between 750 and 5,000,

of maleic anhydride and diisobutylene in approximately equimolecular proportions and mixtures of such copolymers, said polymeric material imparting to a 35% solution thereof in an organic solvent therefor selected from the class consisting of dioxane and methyl ethyl ketone a viscosity less than 1,000 centipoises at 25 C., the suspension having a pH between 4.5 and 12.

No references cited. 

1. A PIGMENT PASTE COMPRISING AN AQUEOUS SUSPENSION OF FINELY DIVIDED WATER-INSOLUBLE PIGMENT DISPERSED WITH AT LEAST ABOUT 0.05%, ON THE WEIGHT OF PIGMENT, OF A POLYMERIC DISPERSANT CONSISTING OF A WATER-SOLUBLE SALT SELECTED FROM THE GROUP CONSISTING OF AMMONIUM AND ALKALI METAL SALTS OF A POLYMERIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF A RELATIVELY HOMOGENEOUS COPOLYMER, HAVING A MOLECULAR WEIGHT BETWEEN 750 AND 5,000 OF MALEIC ANHYDRIDE AND DISOBUTYLENE IN APPROXIMATELY EQUIMOLECULAR PROPORTIONS AND MIXTURES OF SUCH COPOLYMERS, SAID POLYMERIC MATERIAL IMPARTING TO A 35% SOLUTION IN AN ORGANIC SOLVENT THEREFOR SELECTED FROM THE CLASS CONSISTING OF DIOXANE AND METHYL ETHYL KETONE A VISCOSITY LESS THAN 1,000 CENTIPOISES AT 25*C., THE SUSPENSION HAVING A PH OF AT LEAST 4.5 TO
 12. 